This invention relates to jet drop printing by a plurality of liquid jets arranged in one or more rows. In the preferred embodiment it relates to jet drop recording with a recording head of the general type shown in Sweet et al. U.S. Pat. No. 3,373,437.
As shown in the Sweet patent a recording liquid is forced through a row of nozzles arranged along a straight line to form a row of liquid jets. These jets are stimulated to break up into uniformally sized and regularly spaced drops, which are selectively deflected and caught in accordance with printing control signals applied to a series of electrodes. Drops which are not so deflected and caught deposit upon a moving web to print an image thereon.
A major problem with recording heads of the Sweet et al type has been the relatively limited resolution available therefrom. This difficulty is caused by physical limitations on the spacing between the jet nozzles and the spacing between switching control devices necessarily required for each jet. Heretofore the only satisfactory solution has been to provide a plurality of rows of such jets and to switch them with appropriate time delays as taught in Taylor et al. U.S. Pat. No. 3,560,641.
Advances in fabrication techniques have progressively shrunk spacing requirements, so that it is now possible to accomplish reasonably good resolution with only two rows of jets as taught in Mathis U.S. Pat. No. 3,701,998. However, the Mathis print head is somewhat complex and has inherent resolution limits.
One technique for obtaining improved resolution from a row of ink jets is to oscillate the nozzles and their control components as taught by Hertz U.S. Pat. No. 3,737,914. However, jet drop print heads tend to be somewhat massive and difficult to oscillate at the frequency required for high resolution. At these frequencies, which may be in the order of about 10 kHz, the print head becomes elastic. Moreover for print heads of the Sweet et al. type it is necessary to stimulate the jets at a frequency which may be an harmonic of the head oscillation frequency. Thus the head oscillation interferes with stimulation.